The management of hypertension in patients with chronic obstructive pulmonary disease (COPD) may be complicated by the adverse effects of several antihypertensive agents on pulmonary function. The safety and antihypertensive efficacy of guanabenz, a centrally acting alpha-adrenergic agonist, were evaluated in 42 patients with asthma and 24 patients with other forms of COPD. Among the 64 patients with data evaluated for efficacy, pretreatment supine diastolic blood pressures (SDBP) were between 90 and 121 mm Hg (mean, 100 mm Hg). The patients were treated for 6 months with guanabenz as sole antihypertensive therapy in doses ranging from 8 to 64 mg/day (mean final dosage, 28 mg/day). At the end of the treatment period, a mean decrease in SDBP of 10 mm Hg was observed (p less than 0.001). Excellent or satisfactory blood pressure responses were obtained for 65% of the asthmatic patients and 83% of the patients with other forms of COPD. Mean supine pulse rate decreased by 7 beats/min (p less than 0.001), and mean body weight decreased by 2 lb. (p less than 0.05). Only one patient discontinued guanabenz treatment because of an exacerbation of asthma thought to be due to airway dryness. Because beta-adrenergic blocking agents, including the cardioselective drugs, have been known to exacerbate COPD, guanabenz treatment may be preferable as antiadrenergic antihypertensive therapy in patients with asthma and other forms of COPD.